Additive for photoresist composition for resist flow process

ABSTRACT

The present invention provides an additive for a photoresist composition for a resist flow process. A compound of following Formula 1 having low glass transition temperature is added to a photoresist composition containing a polymer which is not suitable for the resist flow process due to its high glass transition temperature, thus improving a flow property of the photoresist composition. As a result, the photoresist composition comprising an additive of Formula 1 can be used for the resist flow process. 
                         
wherein, A, B, R and R′ are as defined in the specification of the invention.

This is a divisional of U.S. application Ser. No. 09/878,803 filed Jun.11, 2001 now U.S. Pat. No 6,770,414.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an additive for a photoresistcomposition for a resist flow process, and a photoresist compositioncomprising the same. In particular, the present invention relates to aphotoresist composition comprising an additive which lowers the glasstransition temperature of the photoresist polymer, and a method forforming a contact hole using the same.

2. Description of the Background Art

Recently, semiconductor devices have been highly integrated. It isdifficult to form a contact hole having a high resolution in lithographyprocess. Currently, a contact hole patterning limit of KrF lithographyis about 0.18 μm. Resist flow is a processing technology for forming afine contact hole which exceeds the resolution of the exposing device.

The resist flow process has recently made remarkable developments and sothat it is now used in mass production processes. The technologygenerally involves an exposure process and a development process. Thisprocess forms a photoresist contact hole having a resolution equal tothat of the exposing device. The process also includes heating thephotoresist to a temperature higher than the glass transitiontemperature of the photoresist which causes the photoresist to flow. Thecontact hole gets smaller by the flow of photoresist until a finecontact hole necessary for the integration process is obtained.

Most of the KrF resists can be flow processed, though having differentprofiles after the flow process. That is, the KrF resist mainlycontaining polyvinylphenol consists of a structure having appropriateT_(g) for the flow. However, a resist used for ArF lithography has sohigh T_(g) that it cannot be flow processed. Especially, cycloolefineresists have a T_(g) over about 200° C., and thus is not suitable forthe resist flow process. An appropriate temperature for the resist flowprocess ranges between the T_(g) of the photoresist polymer and adecomposition temperature (T_(d)) where the polymer starts to bedecomposed. Therefore, the polymer having high T_(g) cannot be used fora resist flow because the T_(g) and T_(d) have only a slight difference.Therefore, there is a need for a modified resist material with asuitable disparity between the T_(g) and T_(d) thereby making itsuitable for resist flow processing.

SUMMARY OF THE DISCLOSURE

An additive for a photoresist composition thereby making it suitable fora resist flow process is disclosed.

Photoresist compositions comprising such additive for a resist flowprocess are also disclosed.

A resist flow process for forming a photoresist pattern using suchphotoresist composition is also disclosed.

A contact hole formation method employing the photoresist pattern formedby the above-described process is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first photoresist pattern obtained in Example 11.

FIG. 2 shows a second photoresist pattern obtained in Example 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an additive for a photoresist compositionfor a resist flow process, and a photoresist composition comprising thesame. In particular, the present invention provides a photoresistcomposition comprising the additive which lowers the glass transitiontemperature of the photoresist polymer, thereby improving a flowproperty of photoresist composition during a resist flow process.

In one particular aspect, the present invention provides an additive offollowing Formula 1 for the photoresist composition which is used for aresist flow process:

wherein, A is H or —OR″,

B is H or —OR′″, and

R, R′, R″ and R′″, are independently substituted or unsubstituted linearor branched C₁–C₁₀ alkyl, substituted or unsubstituted linear orbranched C₁–C₁₀ alkoxyalkyl, substituted or unsubstituted linear orbranched C₁–C₁₀ alkylcarbonyl, or substituted or unsubstituted linear orbranched C₁–C₁₀ alkyl containing at least one hydroxyl group (—OH).

Exemplary additives of Formula 1 include, but are not limited to, thefollowing compounds of Formulas 2 to 7:

Another aspect of the present invention provides a photoresistcomposition comprising a photoresist polymer, a photoacid generator, anorganic solvent and the additive of Formula 1.

The present photoresist composition comprising the additive of Formula 1is suitable for the resist flow process. As described above, aphotoresist polymer having very high glass transition temperature(T_(g)) cannot be used for resist flow process since the T_(g) anddecomposition temperature (T_(d)) have only a slight difference.However, the additive of Formula 1 serves to lower the T_(g), thusimproving a flow property of the photoresist composition. As a result,the photoresist composition can be suitably employed for the resist flowprocess.

The photoresist polymer of the photoresist composition can be anycurrently known chemically amplified photoresist polymer disclosed inU.S. Pat. No. 5,212,043 (May 18, 1993), WO 97/33198 (Sep. 12, 1997), WO96/37526 (Nov. 28, 1996), EP 0 794 458 (Sep. 10, 1997), EP 0789 278(Aug. 13, 1997) and U.S. Pat. No. 6,132,926 (Oct. 17, 2000). It ispreferable that the PR polymer be prepared by radical additionalpolymerization of cycloolefin comonomers and the ring structures of thecycloolefin comonomers remains in the main chain of the PR polymer. Anexemplary photoresist polymer employed in the photoresist compositionincludes a compound of following Formulas 8 or 9:

wherein, R₁ is an acid labile protecting group;

R₂ is hydrogen;

R₃ is hydrogen, substituted or unsubstituted linear or branched C₁–C₁₀alkyl, substituted or unsubstituted linear or branched C₁–C₁₀alkoxyalkyl, or substituted or unsubstituted linear or branched C₁–C₁₀alkyl containing at least one hydroxyl -group (—OH);

n is an integer from 1 to 5; and

w, x, y and z individually denote the mole ratio of each monomer,preferably with proviso that w+x+y=50 mol %, and z is 50 mol %.

The acid labile protecting group can be any of the known protectivegroups that can be substituted by an acid and functions to prevent thecompound to which the group is bound from dissolving in the alkalinedeveloper solution. Conventional acid labile protecting groups aredisclosed in U.S. Pat. No. 5,212,043 (May 18, 1993), WO 97/33198 (Sep.12, 1997), WO 96/37526 (Nov. 28, 1996), EP 0 794 458 (Sep. 10, 1997), EP0789 278 (Aug. 13, 1997) and U.S. Pat. No. 6,132,926 (Oct. 17, 2000).Preferable acid labile protecting groups are selected from the groupconsisting of tert-butyl, tetrahydropyran-2-yl, 2-methyltetrahydropyran-2-yl, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl, 1-methoxypropyl, 1-methoxy-1-methylethyl,1-ethoxypropyl, 1-ethoxy-1-methylethyl, 1-methoxyethyl, 1-ethoxyethyl,tert-butoxyethyl, 1-isobutoxyethyl and 2-acetylmenth-1-yl.

Preferably, the photoresist polymer of Formulas 8 or 9 include, but arenot limited to, compounds of Formulas 10 to 13:

The additive of Formula 1 is used in an amount of 1 to 70% by weight ofthe photoresist polymer employed.

Any of known photoacid generator, which is able to generate acids bylight, can be used in photoresist composition of the present invention.Conventional photoacid generators are disclosed in U.S. Pat. No.5,212,043 (May 18, 1993), WO 97/33198 (Sep. 12, 1997), WO 96/37526 (Nov.28, 1996), EP 0 794 458 (Sep. 10, 1997), EP 0789 278 (Aug. 13, 1997) andU.S. Pat. No. 6,132,926 (Oct. 17, 2000).

Preferred photoacid generators include sulfides or onium type compounds.In one particular embodiment of the present invention, the photoresistgenerator is at least one compound selected from the group consisting ofdiphenyl iodide hexafluorophosphate, diphenyl iodide hexafluoroarsenate,diphenyl iodide hexafluoroantimonate, diphenyl p-methoxyphenyl triflate,diphenyl p-toluenyl triflate, diphenyl p-isobutylphenyl triflate,diphenyl p-tert-butylphenyl triflate, triphenylsulfoniumhexafluororphosphate, triphenylsulfonium hexafluoroarsenate,triphenylsulfonium hexafluoroantimonate, triphenylsulfonium triflate anddibutylnaphthylsulfonium triflate. The photoacid generator is used in anamount ranging from about 0.01 to about 10% by weight of the photoresistpolymer employed.

While a variety of organic solvents, disclosed in U.S. Pat. No.5,212,043 (May 18, 1993), WO 97/33198 (Sep. 12, 1997), WO 96/37526 (Nov.28, 1996), EP 0 794 458 (Sep. 10, 1997), EP 0789 278 (Aug. 13, 1997) andU.S. Pat. No. 6,132,926 (Oct. 17, 2000), are suitable for use in thephotoresist composition of the present invention, the organic solventselected from the group consisting of propyleneglycol methyl etheracetate, ethyl lactate, methyl 3-methoxypropionate,ethyl-3-ethoxypropionate and cyclohexanone is preferred. The amount ofsolvent used is preferably in the range of from about 100% to 1000% byweight of the photoresist polymer.

A process is also disclosed for forming a photoresist pattern, byintroducing the resist flow process and using the photoresistcomposition containing the additive of Formula 1.

The process for forming the photoresist pattern comprises the steps of:

(a) coating the above described photoresist composition containing theadditive of Formula 1 on a substrate to form a photoresist film;

(b) forming a first photoresist pattern using a lithography process(preferably the first photoresist pattern has a lower resolution thanthe maximum resolution of an exposing device); and

(c) producing a second photoresist pattern from the first photoresistpattern using a resist flow (i.e., flow bake) process.

Preferably, the second photoresist pattern has a higher resolution thanthe first photoresist pattern. More preferably, the second photoresistpattern,has a higher resolution than the maximum resolution of theexposing device of the step (b).

The temperature of the resist flow process of step (c) is preferably inthe range of from about 120 to about 190° C.

A method is also disclosed for preparing a contact hole using thephotoresist composition described above. In particular, a substratecoated with the photoresist composition of the present invention isetched using the second photoresist pattern (as described above) as anetching mask to form the contact hole.

Yet another embodiment provides a semiconductor element that ismanufactured using the photoresist composition described above.

The present invention will now be described in more detail by referringto the examples below, which are not intended to be limiting.

I. Synthesis of Additive

EXAMPLE 1 Synthesis of Compound of Formula 2

To tetrahydrofuran was added 0.1 mole of lithocholic acid and 0.1 moleof triethylamine, and the resulting solution was maintained at atemperature below 4° C. in an ice bath. 0.12 mole of acetyl chloride wasslowly added thereto, and the resulting solution was reacted for 8hours. Thereafter, residual solvent was removed by using a vacuumdistillator. A compound was extracted by using ethyl acetate, and washedwith water a few times, to obtain 3α-acetylcholanic acid. Totetrahydrofuran was added 0.2 mole of 3α-acetylcholanic acid thusobtained and 0.3 mole of acetic anhydride. 0.21 mole of tert-butanol wasadded to the resulting solution. Then, the resulting solution wasreacted for 12 hours, to obtain 3α-acetyl tert-butyl lithocholate offormula 2 (yield: 68%).

EXAMPLE 2 Synthesis of Compound of Formula 3

To tetrahydrofuran was added 0.1 mole of lithocholic acid and 0.1 moleof triethylamine, and the resulting solution was maintained at atemperature below 4° C. in an ice bath. 0.12 mole of acetyl chloride wasslowly added thereto, and the resulting solution was reacted for 8hours. Thereafter, residual solvent was removed by using a vacuumdistillator. A compound was extracted by using ethyl acetate, and washedwith water a few times, to obtain 3α-acetylcholanic acid. Totetrahydrofuran was added 0.2 mole of 3α-acetylcholanic acid thusobtained and a slight amount of p-toluensulfonic acid. 0.21 mole ofethylvinylether was added to the resulting solution. Then, the resultingsolution was reacted for 12 hours, to obtain 3α-acetylethoxyethyllithocholate of formula 3 (yield: 70%).

EXAMPLE 3 Synthesis of Compound of Formula 4

To tetrahydrofuran was added 0.1 mole of lithocholic acid and 0.1 moleof triethylamine, and the resulting solution was maintained at atemperature below 4° C. in an ice bath. 0.24 mole of acetyl chloride wasslowly added thereto, and the resulting solution was reacted for 8hours. Thereafter, residual solvent was removed by using a vacuumdistillator. A compound was extracted by using ethyl acetate, and washedwith water a few times, to obtain 3α,10α-diacetylcholanic acid. Totetrahydrofuran was added 0.2 mole of 3α,10α-diacetylcholanic acid thusobtained and 0.3 mole of acetic anhydride. 0.21 mole of tert-butanol wasadded to the resulting solution. Then, the resulting solution wasreacted for 12 hours, to obtain 3α,10α-diacetyl tert-butyl lithocholateof formula 4 (yield: 69%).

EXAMPLE 4 Synthesis of Compound of Formula 5

The procedure of Example 2 was repeated but using3α,10α-diacetylcholanic acid obtained in Example 3, instead of3α-acetylcholanic acid, to obtain 3α,10α-diacetylethoxyethyllithocholate of formula 5 (yield: 72%).

EXAMPLE 5 Synthesis of Compound of Formula 6

To tetrahydrofuran was added 0.1 mole of lithocholic acid and 0.1 moleof triethylamine, and the resulting solution was maintained at atemperature below 4° C. in an ice bath. 0.36 mole of acetyl chloride wasslowly added thereto, and the resulting solution was reacted for 8hours. Thereafter, residual solvent was removed by using a vacuumdistillator. A compound was extracted by using ethyl acetate, and washedwith water a few times, to obtain 3α,5α,10α-triacetylcholanic acid. Totetrahydrofuran was added 0.2 mole of 3α,5α,10α-triacetylcholanic acidthus obtained and 0.3 mole of acetic anhydride. 0.21 mole oftert-butanol was added to the resulting solution. Then, the resultingsolution was reacted for 12 hours, to obtain 3α,5α,10α-triacetyltert-butyl lithocholate of formula 6 (yield: 70%).

EXAMPLE 6 Synthesis of Compound of Formula 7

The procedure of Example 2 was repeated but using3α,5α,10α-triacetylcholanic acid obtained in Example 5, instead of3α-acetylcholanic acid, to obtain 3α,5α,10α-triacetylethoxyethyllithocholate of Formula 7 (yield: 71%).

II. Synthesis of Photoresist Polymer

PREPARATION EXAMPLE 1 Synthesis of Poly(tert-butyl5-norbornene-2-carboxylate/2-hydroxyethyl5-norbornene-2-carboxylate/5-norbornene-2-carboxylic acid/maleicanhydride)

To tetrahydrofuran or toluene was added 0.5 to 0.95 mole of tert-butyl5-norbornene-2-carboxylate, 0.05 to 0.8 mole of 2-hydroxyethyl5-norbornene-2-carboxylate, 0.01 to 0.2 mole of5-norbornene-2-carboxylic acid, 0.5 to 1 mole of maleic anhydride and0.5 to 10 g of 2,2′-azobisisobutyronitrile (AIBN).

The mixture was stirred at 60 to 70° C. for 4 to 24 hours under annitrogen or argon atmosphere. The resulting polymer was precipitated inethyl ether or hexane, and dried to obtain the title polymer of Formula10.

PREPARATION EXAMPLE 2 Synthesis of Poly(tert-butyl5-norbornene-2-carboxylate/3-hydroxypropyl5-norbornene-2-carboxylate/5-norbornene-2-carboxylic acid/maleicanhydride)

The procedure of Preparation Example 1 was repeated but using3-hydroxypropyl 5-norbornene-2-carboxylate, instead of 2-hydroxyethyl5-norbornene-2-carboxylate, to obtain the title polymer of Formula 11.

PREPARATION EXAMPLE 3 Synthesis of Poly(tert-butyl5-norbornene-2-carboxylate/2-hydroxyethyl5-norbornene-2-carboxylate/5-norbornene-2,3-dicarboxylic acid/maleicanhydride)

The procedure of Preparation Example 1 was repeated but using5-norbornene-2,3-dicarboxylic acid, instead of 5-norbornene-2-carboxylicacid, to obtain the title polymer of Formula 12.

III. Preparation of Photoresist Composition

EXAMPLE 7

To propyleneglycol methyl ether acetate (100 g) was added the polymer offormula 10 (10 g), the compound of formula 2 (0.2 g), andtriphenylsulfonium triflate (0.1 g). The mixture was then stirred andfiltered through a 0.20 μm filter to obtain a photoresist composition.

EXAMPLE 8

To propyleneglycol methyl ether acetate (100 g) was added the polymer offormula 11 (10 g), the compound of formula 3 (0.2 g), andtriphenylsulfonium triflate (0.1 g). The mixture was then stirred andfiltered through a 0.20 μm filter to obtain a photoresist composition.

EXAMPLE 9

To propyleneglycol methyl ether acetate (100 g) was added the polymer offormula 12 (10 g), the compound of formula 4 (0.2 g), andtriphenylsulfonium triflate (0.1 g). The mixture was then stirred andfiltered through a 0.20 μm filter to obtain a photoresist composition.

EXAMPLE 10

To propyleneglycol methyl ether acetate (100 g) was added the polymer offormula 13 (10 g), the compound of formula 7 (0.2 g), andtriphenylsulfonium triflate (0.1 g). The mixture was then stirred andfiltered through a 0.20 μm filter to obtain a photoresist composition.

IV. Formation of Photoresist Pattern

EXAMPLE 11

The photoresist composition prepared in Example 7 was coated on a wafer,baked at 100° C. for 90 seconds and exposed to light using a 0.60NA KrFexposing device (Nikon S201). The photoresist composition was post-bakedat 130° C. for 90 seconds and developed in 2.38 wt % aqueous TMAHsolution to obtain a 200 nm L/S pattern (see FIG. 1). The resultingpattern was flow baked at 153° C. for 90 seconds to obtain a 150 nm L/Spattern (see FIG. 2).

EXAMPLE 12

The procedure of Example 11 was repeated but using the photoresistcomposition prepared in Example 8, to obtain a 130 nm L/S pattern.

EXAMPLE 13

The procedure of Example 11 was repeated but using the photoresistcomposition prepared in Example 9, to obtain a 100 nm L/S pattern.

EXAMPLE 14

The procedure of Example 11 was repeated but using the photoresistcomposition prepared in Example 10, to obtain a 150 nm L/S pattern.

As discussed earlier, the additive of the present invention improves theflow property of the photoresist polymer for ArF which is not suitablefor the resist flow process due to its high glass transitiontemperature, thus enabling the photoresist composition to be easilythermally flown. That is, the photoresist composition containing theadditive can be suitably employed for the resist flow process forforming the contact hole.

The foregoing discussion of the invention has been presented forpurposes of illustration and description. The foregoing is not intendedto limit the invention to the form or forms disclosed herein. Althoughthe description of the invention has included description of one or moreembodiments and certain variations and modifications, other variationsand modifications are within the scope of the invention, e.g., as may bewithin the skill and knowledge of those in the art, after understandingthe present disclosure. It is intended to obtain rights which includealternative embodiments to the extent permitted, including alternate,interchangeable and/or equivalent structures, functions, ranges or stepsto those claimed, whether or not such alternate, interchangeable and/orequivalent structures, functions, ranges or steps are disclosed herein,and without intending to publicly dedicate any patentable subjectmatter.

1. A resist flow process for forming a photoresist pattern comprisingthe steps of: (a) forming a first photoresist pattern on a substrateusing a photoresist composition comprising a photoresist polymer, aphoto acid generator, an organic solvent, and an additive selected fromthe group consisting of compounds of the following Formulas 3 to 7:

wherein said photoresist polymer is a compound selected from the groupconsisting of the following Formulas 8 and 9:

wherein, R₁ is an acid labile protecting group: R₂ is hydrogen; R₃ isselected from the group consisting of hydrogen, C₁–C₁₀ alkyl, C₁–C₁₀alkoxyalkyl, and C₁–C₁₀ alkyl containing at least one hydroxyl group(—OH); n is an integer from 1 to 5; and w+x+y=50 mol %, and z is 50 mol%; and (b) performing resist flow process onto the first photoresistpattern to obtain a second photoresist pattern.
 2. The resist flowprocess according to claim 1, wherein said step (a) further comprisesthe steps of: (i) coating said photoresist composition on said substrateto form a photoresist film, wherein said substrate is a semiconductordevise; and (ii) producing said first photoresist pattern using alithography process.
 3. The resist flow process according to claim 1,wherein said first and second photoresist pattern comprises a contacthole pattern.
 4. The resist flow process according to claim 1, whereinsaid resist flow process comprises heating to a temperature between Tgof photoresist polymer and a decomposition temperature (T_(d)) where thepolymer starts to be decomposed.
 5. The resist flow process according toclaim 1, wherein said additive is present in an amount ranging from 1 wt% to 70 wt % of the photoresist polymer.
 6. The resist flow processaccording to claim 1, wherein said photoacid generator is selected fromthe group consisting of diphenyl iodide hexafluorophosphate, diphenyliodide hexafluoroarsenate, diphenyl iodide hexafluoroantimonate,diphenyl p-methoxyphenyl triflate, diphenyl p-toluenyl triflate,diphenyl p-isobutylphenyl triflate, diphenyl p-tert-butylphenyl inflate,triphenylsulfonium, hoxafluororphosphate, triphenylsulfoniumhexafluoroarsenate, triphenylsulfonium hexafluoroantimonate,triphenylsulfonium triflate, dibutylnaphthylsulfonium triflate, andmixtures thereof.
 7. The resist flow process according to claim 1,wherein said photoacid generator is present in an amount ranging from0.01 wt % to 10 wt % of the photoresist polymer.
 8. The resist flowprocess according to claim 1, wherein said organic solvent is selectedfrom the group consisting of propyleneglycol methyl ether acetate, ethyllactate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate andcyclohexanone.
 9. The resist flow process according to claim 1, whereinsaid organic solvent is present in an amount ranging from 100 wt % to1000 wt % of the photoresist polymer.
 10. A resist flow process forforming a photoresist pattern comprising the steps of: (a) forming afirst photoresist pattern on a substrate using a photoresist compositioncomprising a photoresist polymer, a photo acid generator, an organicsolvent, and an additive selected from the group consisting of compoundsof following Formulas 3 to 7:

(d) performing a resist flow process onto the first photoresist patternto obtain a second photoresist pattern, wherein said photoresist polymeris selected from the group consisting of the following Formula 10 to 13:


11. The resist flaw process according to claim 10, wherein step (a)further comprises the steps of: (i) coating said photoresist compositionon said substrate to form a photoresist film, wherein said substrate isa semiconductor device; and (ii) producing said first photoresistpattern using a lithography process.
 12. The resist flow processaccording to claim 10, wherein said first and second photoresist patterncomprises a contact hole pattern.
 13. The resist flow process accordingto claim 10, wherein said resist flow process comprises heating to atemperature between Tg of the photoresist polymer and a decompositiontemperature (T_(d)) where the polymer starts to be decomposed.
 14. Theresist flow process according to claim 10, wherein said additive ispresent in an amount ranging from 1 wt % to 70 wt % of the photoresistpolymer.
 15. The resist flow process according to claim 10, wherein saidphotoacid generator is selected from the group consisting of diphenyliodide hexafluorophosphate, diphenyl iodide hexafluoroarsenate, diphenyliodide hexafluoroantimonate, diphenyl p-methoxyphenyl triflate, diphenylp-toluenyl triflate, diphenyl p-isobutylphenyl triflate, diphenylp-tert-butylphenyl triflate, triphenylsulfonium hexafluororphosphate,triphenylsulfonium hexafluoroarsenate, triphenylsulfoniumhexafluoroantimonate, triphenylsulfonium triflate,dibutylnaphthylsulfonium triflate, and mixtures thereof.
 16. The resistflow process according to claim 10, wherein amid photoacid generator ispresent in an amount ranging from 0.01 wt % to 10 wt % of thephotoresist polymer.
 17. The resist flow process according to claim 10,wherein said organic solvent is selected from the group consisting ofpropyleneglycol methyl ether acetate, ethyl lactate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate and cyclohexanone.
 18. Theresist flow process according to claim 10, wherein said organic solventis present in an amount ranging from 100 wt % to 1000 wt % of thephotoresist polymer.